Communication systems are known to include controlling infrastructure and end-user equipment, also known as subscriber units or communication units, such as mobile and portable communication units. The controlling infrastructure may be a wire-line controlling infrastructure such as a local area network, a wide area network, the public switching telephone network (PSTN), the Internet, and so forth. In a wireline system, subscriber units are personal computers, workstations, personal agents, and any other telephone devices, facsimile machines, and so forth. Alternatively, the controlling infrastructure may be for a wireless communications system wherein the controlling infrastructure includes a zone controller or system controller, site controllers or base station controllers, base stations, and a plurality of communication channels. In a wireless system, the subscriber units may be land mobile radios, cellular telephones, pagers, personal computers equipped with wireless transceivers, and personal digital assistants equipped with wireless transceivers.
In a wireless system, which may be a digital system or analog system, the subscriber units may transceive voice information and/or data information. To transceive voice information, an initiating subscriber unit transmits an inbound signaling word (ISW) to the controlling wireless infrastructure, wherein the ISW is requesting access to a voice channel. The request may be for a one-to-one communication, such as a typical telephone call, or a one-to-many communication such as a group call. Upon receiving the inbound signaling word, the controlling wireless infrastructure determines whether the requesting subscriber unit is authorized to make such a request and whether the request can be accommodated. To determine whether the requesting subscriber unit is authorized to make the particular request, the controlling infrastructure accesses a home location register (HLR) to determine which services the requesting subscriber unit has subscribed to. If the HLR indicates that the requesting subscriber unit is authorized to make such a request, the request will be granted. To determine whether the request can be fulfilled, the controlling wireless infrastructure determines whether a wireless communication channel is available in the site of the requesting subscriber unit. The wireless controlling infrastructure also determines whether communication channels are available in other sites in which targeted subscriber units (i.e., subscriber units that are identified as a recipient of the communication) are located.
If a subscriber unit involved in a digital voice communication desires to request data, the subscriber unit must leave any voice communication it is involved in (i.e., de-affiliate from the voice channel supporting the voice communication) and return to the control channel. Once affiliated with the control channel, the subscriber unit transmits an inbound signaling word requesting the data. If the request is to be fulfilled, the subscriber unit receives, via the control channel, an outbound signaling word, which indicates a data channel. The subscriber unit then affiliates with the data channel to receive the requested data. While the subscriber unit is awaiting its data request to be fulfilled, it misses potentially vital information because it is no longer affiliated with the voice communication.
For example, assume that a group of police officers are involved in a group communication responding to an emergency situation. Based on the facts surrounding the emergency situation, one of the officers involved desires additional data that needs to be shared with the group of officers involved in the emergency situation. To obtain this data, the requesting subscriber unit operated by the police officer would have to disengage from the voice channel, return to the control channel to request the data and then affiliate with a data channel to receive the data. Since only the requesting officer would receive the data, the officer must return to the talk group channel and verbally communicate the received data.
Therefore, a need exists for a method and apparatus that allows subscriber units to request and receive data for itself and/or for its group without having to leave a voice communication.